At least 12 people, including some elderly and children, were injured Wednesday night when a duplex exploded and shook a Dorchester neighborhood after a possible gas leak, authorities said.

The blast at 27 Hansborough St. erupted into a three-alarm fire that left two elderly residents with critical injuries and numerous families evacuated from their nearby homes, authorities said.

Steve MacDonald, a Fire Department spokesman, said nine people inside the home were injured and three others who were outside suffered wounds that may have been caused by flying debris or shattered glass.

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Mike Bosse, a deputy superintendent with Boston Emergency Medical Services, said two of those inside the home were elderly people who were critically injured and had significant burns. They were taken to Brigham and Women’s Hospital, but there was no information on their conditions early Thursday morning.

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Fire officials said those with the less serious injuries included adults and children who were taken to area hospitals.

Dorothy Robinson, who lives near the house, said she was in her living room watching TV when a thunderous blast rattled the neighborhood.

“It sounded like an earthquake,” said Robinson, 62. “I was just so frightened. I couldn’t believe it. I don’t know if I will be able to sleep tonight.”

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Jean Reynolds, 64, said the blast shook her home three houses away.

“I heard a big ‘boom,’” she said. “I thought it was an airplane, it was so loud.”

Interim Fire Commissioner John Hasson said shortly after 10 p.m. that the three-alarm fire was knocked down and the house was “just barely” standing and off its foundation.

He said officials were investigating whether a gas leak caused the blast.

According to Hasson, the explosion occurred at about 9:20 p.m. and one adjacent home was also damaged by the impact. Hansborough Street was then shut down.

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Chris Milligan, a spokeswoman for National Grid, the natural gas utility, issued a statement Wednesday night expressing sympathy for the injured.

“We are currently working with emergency responders and local officials,” she said. “The cause of this incident currently is under investigation.”

MacDonald said National Grid was on the scene before the fire because of reports of a gas odor.

Mayor Martin J. Walsh and Boston Police Commissioner William Evans arrived at the scene, asking if any other families needed shelter.

With many residents displaced, the city brought in MBTA buses to keep evacuated residents warm until temporary shelter was available, Walsh said.

One side of the street was completely evacuated and residents huddled outside waiting for buses, some without socks, covered by blankets they grabbed as they left their homes.

One group of evacuees was taken to the Greater Boston Adult Day Health Center on Livingstone Street, a community gathering spot for Haitian Americans.

There, families gathered around tables decorated in pink, green, and gold tablecloths as they tried to come to terms with the night’s events. More than three dozen families affected by the fire came through over the course of the evening, a center employee said.

Sitting on a leather sofa there, Sunday Idahor recalled running downstairs and then quickly back upstairs after the blast, yelling, “Gas! Gas! Gas!’’ as his family hurried outdoors.

Everyone poured into the street, including a young man who said his mother-in-law was still in the burning house.

Idahor said he and another man ran inside and found the woman on the floor in a back bedroom.

“There was blood all over her face,’’ he said. “She could barely move.”

They lifted the woman and carried her outside, where firefighters took over.

“It was just horrible,’’ he said.

Fire spokesman MacDonald said all residents were expected to be able to return home within hours, except those in the house that exploded and the residents next door at 23 Hansborough St.

Jacqueline Jones, 47, said she heard a boom and then ran downstairs to see flames and smoke shooting out of the three-family home.

She said she saw a teenager who had run out of the house, and he told her that he smelled gas before the explosion.

One resident was overcome with emotion.

Carla Leiva, 25, had been in her bedroom in a home next to the duplex when she heard an explosion, and when she looked outside the window she saw flames rising into the night sky.

“I felt the house shaking,’’ she said, as she stood outside Wednesday night, shaking, with tears in her eyes. “There was hot air coming into my house.”